Many wireless communication systems require a rapid deployment of independent mobile users as well as reliable communications between user nodes. Mesh networks are based on self-configuring autonomous collections of portable devices that communicate with each other over wireless links having limited bandwidths. A mesh network is a collection of wireless nodes or devices organized in a decentralized manner to provide range extension by allowing nodes to be reached across multiple hops. In a mesh network, communication packets sent by a source node thus can be relayed through one or more intermediary nodes before reaching a destination node. Mesh networks may be deployed as temporary packet radio networks that do not involve significant, if any, supporting infrastructure. Rather than employing fixed base stations, in some mesh networks each user node can operate as a router for other user nodes, thus enabling expanded network coverage that can be set up quickly, at low cost, and which is highly fault tolerant. In some mesh networks, special wireless routers also may be used as intermediary infrastructure nodes. Large networks thus can be realized using intelligent access points (IAPs), also known as gateways or portals, which provide wireless nodes with access to a wired backhaul or wide area network (WAN).
Mesh networks can provide critical communication services in various environments involving, for example, emergency services supporting police and fire personnel, military applications, industrial facilities and construction sites. Mesh networks are also used to provide communication services in homes, in areas with no basic telecommunications or little broadband infrastructure, and in areas with demand for high speed services (e.g., universities, corporate campuses, and dense urban areas).
A typical mesh network comprises three types of nodes: intelligent access points (IAPs), access points (APs), and stations (STAs). An IAP generally has access to a backhaul network and provides data service to one or more APs. Each AP then provides data service to various STAs, such as handheld radios or other standard Institute of Electrical and Electronics Engineers (IEEE) 802.11 devices. (Note: for any IEEE standards recited herein, see: http://standards.ieee.org/getieee802/index.html or contact the IEEE at IEEE, 445 Hoes Lane, PO Box 1331, Piscataway, N.J. 08855-1331, USA.) An AP generally can connect to an IAP directly or through a multi-hop route. To maintain a connection, an IAP and its associated APs/STAs generally operate over the same radio channel.
When an AP (for example, a mesh node in a command vehicle operating at an incident scene) moves, it may need to conduct a handoff process (i.e., disassociate from a current mesh network and associate with another mesh network). Because different mesh networks can operate on different channels, the AP generally first conducts a scan to identify the operating channel of another mesh network to which it can become associated. The moving AP often needs to quickly select a channel to complete the handoff process without losing connectivity.
A scan process generally requires an AP to switch to another channel and listen for beacon signals sent from available IAPs. Because multiple channels are often available to a network deployment, a considerable amount of time may be required to scan all possible channels and select a suitable candidate. One way to complete such a long scan process is to begin the scan process well before a handoff process. Then, when the handoff process starts, the AP can quickly select a channel based on the information collected from the previous scan.
However, to scan a non-operating channel to listen for beacon signals, an AP generally must temporarily stop communicating over the current communication channel, which may cause a serious service interruption of the communication channel. Accordingly, there is a need for an improved device and method for frequency scanning.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.